Preservative treatment of vegetable produce



Oct. 11, 1960 a. E. WILLIAMS PRESERVATIVE TREATMENT OF VEGETABLE PRODUCE Filed Oct. 11. 1957 8 URNER COOL EH WCUUM COOL [N6 0 M M L M E U R M B PRESERVATIVE TREATMENT OF VEGETABLE rnonucn I Beverly E. Williams, Hillsborough, Calif., assignor to Hodges Research and Development. Company, New York, N.Y., a corporation of California Filed on. 11, 1957, Ser. No 68 9 ,58'3

s Claims. (Cl. 93-154 7 This invention has to'do with the treatment or process-.

ing of vegetable produce with substantially oxygen-free gases for preservation of the produce during shipment and distribution, and is directed to improved methods whereby benefits of such treatment can be realized to better and longer advantage than has been possible by treatments of this type heretofore proposed. The invention is particularly concerned with the preservation of leafy vegetables such as lettuce, cabbage, broccoli and the like which present large surface areas, much of which are so confined within the leaf structures as to be diflicultly accessible to preservative gasesapplied in the usual manners. tion of lettuce, in reference to which a typical adaptation of the invention will be described.

It has been found that oxygen-free gases, particularly combustion gases consisting essentially of carbon monoxide and nitrogen, may be used to advantage in maintain- Such conventional proposals have been found to involve inherent limitations in the extent or degree to which air contacting all the surfaces of the produce, can be re: placed with a non-oxidizing gas, and the temporary duration of the treatment because of uninhibited access of air thereafter to the treated surfaces. As indicated, entry of the treating gas to the innermost regions of the produce, is resisted by the air present, and such initially beneficial effects that may have been gained, tend to be soon lost because of further dilution by the atmospheric air.

The present invention has for one of its major objects to accomplish initially a more complete penetration, distribution, and concentration of the treating gas within each piece of the leafy produce, by preceding the gas treatment with evacuation of air from the, produce to a degree that will permit gas entry to the innermost surfaces, and therefore establish a degree of surface contact and penetration favorable to prolonged retention of the gas. For purposes of evacuation, I prefer to subject the packed produce to deaeration by methods of the kind commonly employed for vacuum cooling of the produce, and involving generally the placement of the produce in a chamber which is rapidly evacuated to very low absolute pressure, usually below mm. of mercury, in a period of time sufiiciently short, say between to 60 minutes, to cause not only evacuation but also cooling of the produce. Upon completion of the evacuation and resulting cooling, the invention contemplates replacement of the evacuated air by a substantially oxygen-free gas, preferably a combustion gas consisting essentially of carbon monoxide Of major practical importance is the preserva and nitrogen, which permeates the produce deeply and uniformly, and at a concentration increased by reason of the cooled condition of the produce.

Further objects of the invention are directed to retention of impregnating gas within each piece of produce, at

concentrations which'will extend its preservative effectiveness over longer periods of time during shipment and distribution of the produce. In accomplishment of this object, the produce during evacuation and gas impregnation, is kept within gaspermeable enclosures about and contacting the pieces of produce. In addition to such' functions as the produce enclosure may have purely forpackaging purposes, the choice and function of the enclosure 'for the purposes of the invention, is to provide permeability that will allow initial exhaustion of air from the produce and its replacement by the treating gas, and further, that degree of enclosure which will resist replacement of the produce-contained gas by atmospheric air.

exhausted from the produce in the cooling treatment andis replaced by the treating gas upon introduction of the latter to the evacuated chamber. By reason of the limited openness or exposure of the producethrough openings of the kind later typified, the gas permeating the pieces of produce tends to resist replacement by air and to remain over long periods at preservative concentrations. I

'The above mentioned as well as other additional features and objects of the invention together with the details of illustrative procedures for practicingthe invention, will be more fully understood from the following detailed description of the accompanying drawing, in

which:

Fig. 1 is a view illustrating diagrammatically and in flow sheet form the facilities employed for vacuum cooling and subsequent gas impregnation of the packaged produce; and

Fig. 2 is a view illustrating a suitable type and form of package for the purpose.

Referring first to Fig. 1, in accordance with known procedures for the vacuum cooling of produce, the latter may be placed on suitable conveyors or truc-ks 10 within a chamber 11 equipped with suitable facilities for evacuat ing the chamber and its contained produce to low pressures, which as indicated, may be well below 10 mm. Hg

absolute. The pieces of produce 12 are shown to be packaged for distribution in fiberboard boxes or cartons 13 which may be provided with relatively small apertures 14 through which air is exhausted from the cartons and contained produce as the evacuation proceeds. The steam ejector 15 communicating with the chamber 11 through line 16 may be regarded as typifying any suitable exhaust-f ing means for evacuating the chamber. g

In the broad contemplation of-theinvention, the m gen-free treating gas may be derived from any suitable source, although from considerations of practicability, it is preferred to use combustion gases resulting from the complete burning of a fuel such as a hydrocarbon within the methane to propane series fed to burner 17 through line 18 together with air supplied through line 19 at a ratio suificient to oxidize the fuel substantially entirely to carbon monoxide and nitrogen with little or no free oxygen remaining in the outlet stream flowing through line 20. The fuel and the conditions of combustion may or may not be so selected and controlled as to leave trace quantities in the eifluent of such hydrocarbons as acetylene and ethylene, or if the latter are desired otherwise,

" distribution.

either or both may be added through line 21 for admixture with the combustion gas in chamber 225- The subj stantially oxygen-free gas so composed, maybe discharged either through valved line 23 for storage in an accumulater z'q-for'delivery through lines 25 and16fito the" chamber 11;01' the gas may be passed through valved line'26 through .cooler 27 1andthence through lines 28 and 25 to the accumulator 24 or through line-16 directly 'As a typical pr'ocedurein practical operation, the packaged produce initiallyis cooled in chamber -11 by evac;

uationof -the latter to' a pressure of fromj4-5 mm. of

minutes Beingrsomewhat moist when initially loaded into the chamben the produce undergoes 'quick cooling by reason of vaporization or the moisture; When the evacuation and cooling are completed, valve 29 is closed x the essentially inert gas is introduced to replace the 7 air evacuated from theproduce and chamber, either from a the accumulator'24' through line 25, or from the cooler dischargerline 28, it being understoodthat in' the latter event, the burner 17 is. inoperation during the period said chamber a'substantially oxygen-free innocuous gas consisting of onrthe order of 85% nitrogen, l2%-carbon dioxide, and,.2% carbon monoxide, said gas being produced by the combustion of propane and butane which is caused by virtue of th'e evacuation to permeate the produce .and by virtue of the enclosures to resist oxygen access to the produce during subsequent shipment and jdistribution. t

,rnereury'absolute within a periodofsay from '30 to'SQ v,

3. The method of'treatingh'esh leafyvegetable produce to improve. its 'lgeeping qualities during shipment and distribution, that includesplacingfthe produce in achamber with gas ,i permeable enclosures about and contacting the pieces'of produce, evacuating the chamber to cool the produce Iandilremove air from within the enclosures, and relieving the vacuum by introducing to said chamber ,a substantially oxygen-free innocuous gas,

consisting essentially of carbon monoxide and nitrogen,

V 7 said gas being produced bythe combustion'of propane and butane which is caused by'virtue of the evacuation to -permeate the produce and by virtuerof the enclosures toxresist oxygen access to the produce during subsequent'shipment anddistribtitio'ng e ating fresh lea'fy vegetable prod l '4. The method of tee to improvefit s;'keeping qualities during shipment and distribution, that includes placing the produce,

packaged in gas permeable'paperboard boxes,'within a beenincreased by reason of the cooled condition of the", I

produce." Thereafter, following removal of the produce wfifoin the cooling chamber, the'fgas tends to remain in a the produce andlto resistreplacement by atmospheric air, due to the {completeness with which the gas has "been 7 caused .to permeate the produce and the limited fr'eedom 1 7 with which'atrnospheric' air can gain access through the,

carton apertures 14 for replacement of the gas. Thus, the overall 'efiect of thetreatment is to assure preservation chamber, evacuating'therchanrber to cool the produce and remove air from within the'enclosur'es, and relieviirg the vacuum; by'introducing to said chambera subof the'desired qualities ,in the produce over the ex- 7 Iclairn:

tended periods required for its shipping and distribution, a

' '91. Themethod o t' treating fresh leafyvegjtable tprodi lice tolirnprove its keeping qualities during shipment and Z, distribution, that includes placingvthe produce in a charm 7 her with gas permeable, enclosures about and contact: 7 w

ingfthe pieceslof produce, evacuating the chamber to;

r coolthe produce and remove airtrorn within thefen- 'f 'closures, and relieving thewacuum byiintr'oducing to,

; said chanlb'er'a substantially oxygen-freeinnocuous gas a consisting of on the' order of $5%1nitro'gen,'l2%fcarbon V V dioxide, and 2% carbonrn'ionoxide, saidigas being. pro- 7 duced by the combustion of propane and-butane which is causedby virtueofthe evacuatiomtoperrneate the 7 produce and by virtueiof the enclosures to resistoxygen access to the producejduring subsequentlshipment and 2. The method of treating fresh lafy vegetable produce to improveits keeping, qualities'during shipment and distribution that includes placing the produce'in a cham berwith gas'permeable enclosures about and contacting the pieces of produce, evacuating the chamber at'an absolute pressure below 10 mm. absolute to cool the prod-, V nce and remove air from, within the, enclosure, and, relieving thevacuurn at said pressure by introducing to st antially oxygen-free innocnousgas consisting essentially ofrcarbon monoxide. andfnitro'gen with about 2% carbon-monoxide, said gas being produced by the' combustionoftpropane and butane Which'iS caused by virtue of the evacuation to permeatethe produce andby virtue of the;enclosures to resist oxygen access' to the produce during subsequent shipment'and distribution.

5 .The method of'treating fresh :leafy vegetable produce to improve its keeping qualities during shipment and {distribution that includes placing the "produce in a V chamber with gaspermeable enclosures about and contacting the pieces ofproduce; evacuating the chamber to cool the produce and remove anfronrwithin the enclo-' sures, and relieving the vacuum in said chambenby in troducing' thereto tatcooled substantiallyroxygen-free"innocuouscomhustion gas, consisting substantiallyof car bon monoxide; and nitrogen 1 containing approxiniately 12% 'ca i ndioxide, said gas being produced by the com-,

, bustion ofprop'aneand butane WhiQh is causedbyyirtuef 1 offthe evacuation to permeatetheiproduce and by virtue ofjth'e enclosures "to' resist oxygen access to the produce 7 duringlsubsequent shipmentand distribution.

'nerei eace's Cited in in the of-this patent 1 (U IT-En STATES PATEN'V'IS'" 2,490,951 Dunldey Dec. 13, 1949 2,542,206 Nichols ''Feb; 20, 1951 2,606,704 Nichols r Aug. '12, 1952 "2 ,634,590 Beardsley 'Apr. 14, 1953 2,684,907 Brunsing July 27, 1954 Blagburn r Feb. '16, 1915 

1. THE METHOD OF TREATING FRESH LEAFY VEGETABLE PRODUCE TO IMPROVE ITS KEEPING QUALITIES DURING SHIPMENT AND DISTRIBUTION, THAT INCLUDES PLACING THE PRODUCE IN A CHAMBER WITH GAS PERMEABLE ENCLOSURES ABOUT AND CONTACTING THE PIECES OF PRODUCE, EVACUATING THE CHAMBER TO COOL THE PRODUCE AND REMOVE AIR FROM WITHIN THE ENCLOSURES, AND RELIEVING THE VACUUM BY INTRODUCING TO AND CHAMBER A SUBSTANTIALLY OXYGEN-FREE INNOCOUS GAS CONSISTING OF ON THE ORDER OF 85% NITROGEN, 12% CARBON DIOXIDE, AND 2% CARBON MONIXIDE, SAID GAS BEING PRODUCED BY THE COMBUSTION OF PROPANE AND BUTANE WHICH IS CAUSED BY VIRTUE OF THE EVACUATION TO PERMEATE THE PRODUCE AND BY VIRTUE OF THE ENCLOSURES TO RESIST OXYGEN ACESS TO THE PRODUCE DURING SUBSEQUENT SHIPMENT AND DISTRIBUTION. 